1. Field of the Invention
The present invention relates to fingerprint ink dispensing apparatus and more particularly to a combined ink pad and reservoir.
2. Description of the Prior Art
The art of fingerprinting and identifying persons by their fingerprints is well known. The simplest method of taking a person's fingerprints is to apply a highly colored ink or dye (hereinafter collectively referred to as "ink") such as a suspension of carbon black particles to the person's fingertips. Subsequent rolling or pressing of the person's fingers on a clean recording surface, such as paper, deposits the ink on the surface in a pattern corresponding to the fingerprints of the person.
To obtain clear prints standard ink is generally squeezed from a tube onto a plate and then rolled to an appropriate thickness. It, of course, takes time to prepare an ink plate. Moreover, if the solvent and pigment separate (which often occurs) additional time is required for the technician to re-mix the constituents on the plate. In addition, it is not unnatural for a person to vary the ink thickness on the plate when rushed etc., with the result that the resulting prints are smeared (too much ink) or too faint (too little ink).
A rigid plate made of ceramic and disposed over a felt reservoir has also been used to apply ink to the fingertips. The ceramic plate had a porosity of between 30% to 35% with an average pore size of about 5 microns in diameter. The ink consisted of carbon black pigment dispensed in a glycerol/glycol/water base with a 22% by weight concentration of the pigment. The average diameter of the pigment particles was about 0.35 microns with the diameter of substantially all of the pigment particles falling within the range of 0.15 to 0.60 microns. This system eliminated the ink plate and the human variables associated with the use of such a plate. However, problems of fingerstaining and penetration rate into the paper (too slow) still existed to some extent. In addition, the ink solution had stability problems. To solve these problems, the glycerol dispersant was replaced with a hydrocarbon based oil and the concentration of the carbon black pigment was reduced to about 14% by weight.
The change of dispersant and pigment concentration, however, resulted in fingerprint images which remained light in contrast and tended to bleed, i.e., the lines of the image broadened and became fuzzy in appearance. These new problems became particularly acute when the recorded prints were read and compared by computerized machines.
The present invention is aimed at solving the above problems.